Surface combustion cracking furnace



Feb. 17, 1948. E. o. BENNETT 2,436,282

SURFACE COMBUSTIION CRCKING FURNACE Filed Maron ze, 194s Patented Feb.17, 1948 UNITED STATE:

SURFACE COMBUSTION CRACKING FURNACE Edwin O.Y Bennett, Ponca City,Okla., assigner to` Continental Oil Company, Ponca'. City, Okla., a

rcorporation of Delaware ApplicationMarch 2s, 1943, serial 10,480,705 Y.

5 canna,`

1 o My invention relates broadly to 'improvements in a method of andapparatusfor cracking fluids, and more particularly to a method of andappa' ratus for cracking a hydrocarbon uid into its constituent parts ofcarbon and hydrogen to produ-ce a superior grade of carbon black.

Carbon black isv made by heating a hydrocarbon fluid in the absence ofair. Heretofore carbon black has been almost-entirely made by either oneof two processes. One of these processes, commonly known as the channelprocess, consists of burning hydrocarbon gas withinsuliicient air in asmoky flame. This operation is conducted in an apparatus having coldAmetall surfaces upon which the flame impinges. Carbon deposited by theame on the metal surfaces is scraped'off and recovered as carbon black'.v

The other process consists of alternately passing hydrocarbon gasthrough a pair v of refractory furnaces which heats the 'gas in theabsence of air. In operation it ishecessary to heat'the refractory ofone furnace while the'gas is being cracked in the other. A reversingswitch is provided in the gas supply line which automaticallyreversesthe iiow of gas when the temperature of the cracking furnacebecomes -too low.

Both of the above processes are inefficient and expensive. The channelprocess yields approximately 1.5 lbs. of carbon black .per 1,000 cubicfeet of gas. The second process is vmore eflicient, but it is also moreexpensive. It yields from 8 to 9 lbs. of carbon black per 1,000 cubicfeet of gas. However, large amountsof fuel are required to heat the hugemass of refractory. Therefractory must be large in order to. minimizethe temperature drop in the furnace during the cracking cycle. Also thereversing switch is com,l plicated and expensive. The yield is far.below the theoretical maximum due to burning of carbon by oxygen whichenters the furnace during the heating cycle. Y l' .An important objectof myinvention is kto pro-y vide a cracking furnace that isparticularlysuitable for making carbon black. r 1

Another object of my invention' is to provide a furnace of the abovementioned character that will maintain the cracking chamber at'aconstant temperature under oxygen-free conditions.

Still another objectof' my invention is to provide a cracking furnace ofthe above 'mentioned character wherein heat is supplied tojth'eicombustion chamber in such away aste prevent the, y cracked materialsfrom depositing-,on the chamberwalls.,

Y other objects and advantages of my invention:

(Cl. 23-277) n f 2 l will be apparent during the course of the followingdescription.

In the drawings forming a part of this specication, and wherein.V likenumerals are employed to designate like parts throughout same,

Fig. 1 is a vertical section Yof a surface combustion cracking furnaceembodying my invention with the control Amechanism shown in elevationand in smaller scale,

the line 2-2 of Fig. 1, and

Fig.3 is a transverse sectional theline 3--3 of Fig. 1, 4

In its broader aspects,- the invention consists of passing hydrocarbongas longitudinally through a porous tube of refractory material, thepassage through which the gas flows being heated by surface combustion.

A combustible mixture under pressure is supplied to a .confined annularspace around the tube. This mixture passes through the tube to theinside thereof where it is ignited and forms a fire-lining covering theinner surfaceof the tube. ,Combustion is complete within a shortdistance of the surface, depending upon the porosity of the tube anddifferential pressure within and outside the tube.- vIn appearance theinner surface ofthe tube is incandescent and no llame, as such, appearsto be present. The mixture is 3.0 regulated. so that all oxygen isconsumed by combustion. No free oxygen entersthe vtube to mix with thefluid being cracked. Temperatures up to 3600 F. are obtainedby thismethod of combustion. Y A.

The iiow of fluid through -the tubeis regulated so that the fluid iscompletely broken up into its component parts. As they pass through thetube, the cracked products are'prevented from adhering to or depositingonthe tube by the continu- 40 ously moving fire-lining. VThesecomponents are easily separatedand collected r`at thedisoharge end -ofthe tube., The carbon. recovered by this method is a superior carbonblack for use in making synthetic rubber. c

More particular1y,rthe invention comprises a surface combustion crackingfurnace having a verticaltube l0 of a refractory material such asCarborundum. The middle Vportion Ia of the tube is porous, and the ends|0b and Ic are pref- 59 erably impervious. The vends of thetube may bemadeimpervious by any suitable means, such as dipping them in aCarborundum sealing cement. v Surrounding tube l0 is a metal housing Il, carried by a suitable supporting structure comprising legs A, ahorizontal supporting plate B and view taken on Fig. 2 is a transversesectional View taken onl triangular gussets C based on the supportingplate and against the sides of the housing H. The housing ll is ofgreater diameter than the tube and supportsthe tube adjacent its upperend. The top la ol.' the housing has a vertical extension or collar lib,which surrounds the projecting end of tube lll. "Packing lf2' retainedin the annular space between'the tube and the collar by the threadedlocking ring I3, provides a pressure tight seal between the tube and theupper end of the housing. l v

Expansion and contraction of tube modated by an expansion joint assemblyon the lower end of the housing. Tubes IPD and l-I areclosed at thebottom by means of an assembly congisting of a plate l5, retaining ringI6 and a slidable sleeve Il. pansion and contraction of the innerrefractory To compensate for uneven eX- tube lll and outer metallic tubeil, there is provided a diaphragm expansion joint I8. The lower half leaof the expansion joint-is welded to sleeve il and the upper half l8b iswelded to tube Il.v

To solidly iifx the lower end of' tube l0 within the cup-shaped portionoiplate l a .bonding material, such 'as' a 'refractory ceramic mortar,nils the space within the :disc surrounding the tube and when set,lxedly holds the tube within the disc. Retaining ring i6 `is threaded tosleeve ll and sets against a shoulder portion of the disc l5 in order'to hold fthe assembly together. 4In operation, elongation or shorteningof either of. the tubes Hl Vor Il different fromv theother tube will becompensated for by this expansion joint.

A combustible mixture, preferably fuel gas and air, is charged Vunderpressure to .the annular space 20 between tube il! and Vhousing Il. Air.

passes through pipe 2l controlled by valve 22 and pressure regulator 23,and gas passes through.

In the form of :the invention shown in Fig. 1,.

ain-opening a iis provided in plate `l5 through which ian ignitiontorchfc'an be inserted to ignite the combustible Ivapors 'withinthetube.. Opening ia is normally closed by a pivoted plate 33. It

is necessary that isuicient pressure be applied to the combustiblemixture -iin lannular 'space 20 to force it inwardly'through"tube 'l 0`at fa 'rategreater than the velocity or *flame 'propagation'outwardlythrough the tube. If this iis done, fall danger oi backfire andexplosion is eliminated. .i

When thefurnaceisred the combustible mixture permeati'ng the "porousvportion lDa of tubel i0 burns at T-the inner surfaceof the tube, whichvbecomes incandescent. Actuallylnoame as such appears within the ltube.This lislrnown assurface ''co'rnbustiorlr Surface combustlonv'in afurnace of this type develops :a higher temperature than can'be obtainedby yany other method. This is due to the completenessof combustion 4andthe intense preheat y-tof which=the air-gas'mixture in annular "space T'is subjected.` Ai-temperature. as

high as 360o F. ihes'ibeen obtained in the iur-- nace illustrated-in theAdrawings. Y

Fluid lto be cracked passesthroughpipe 34 `irito the lowerVend-loitube-itil. li'pe "34 is controlled by valves V'arid lsoperatedby pressure regulators 31 and 38; `.As indicated by the double lead linefor each "of the reference numerals 30 and 34, the` said pipes indicatedthereby extend continuously to the annular chamber 20 and to theinterior of conduit i0 respectively, without opening to the atmosphere.Y

The temperature to which the iiuid will be raised is controlled orregulated by adjusting the amount of combustible mixture supplied to theratio of combustible mixture to the fluid must be accurately regulated.This is done automatically by the'diiferental pressure regulator 39 inpipe 4D, which connected at its ends to pipes 3 0 and 34.' Dierentialpressure regulator 39 operates valve 4l vin pipe 30 to pass an amount offuel to 4the combustion tube proportioned to the quantity of `fluid tobe .cracked The temperature to which the iluid will be raised is alsodependent upon the time required topass it through tube Hl. 'I-Iowever,the rate of ilow of the iluidA through the tube is automatically.regulated by the pressure. `at which it enters the furnace and by thelength of the i'lrekv zone of tube i0. It is obvious *that Vthe.preSS\1.-rc,at Ywhich the fluid enters the 1f uijnzaqx; as well` as ythevratio of iluid tol combustible mixture be accurately and automaticallycontrolledy by the pressure regulaters and meters controlling flowthrough the re- Snectve Supply 1.11185- YSince the combustible mixtureiS Supplied t0 the inside `ofntube vi l) .from the outside thereof, theViluid Passing through the tube has n0 effect upon the burning action ofthe mixture. Furthermore, the fluid is prevented from adhering to ordepositing o n the inner suriac'e of tube lil bythecontinuouslymoving..rirelining As the fluid passes through the tube itisCracked or `physically disrupted into lts-component parts. The crackedfluid together with the products :of combustion pass' out `of .thefurnacethrough stack 42 bolted to the topgofi housing li. The gasesentering stack 42 are :cooled by the water jacket 43 and -quenchingiluids "such asstearri `.or Water introduced intdtire stack through.lateral pipes 44 andc45. Anyv suitable means may be provided to recoverand separate the :cracked components of the -iluid. When vthej-urnace-isused to produce carbon. black, the free carbon vis preferably recoveredbyimeans of :an electrostatic :precipitator or by vsuitable ii'lterswhich are connected to thev discharge end-.of the .furnace shown as thestack 42.. The 'facilities l:for controlling the temperatureYandfcornliustion :condition permit the manufacture -of la fcarbon1black particularly adapted for yuse 'in` rubber manufacture, `.eithernatural or synthetic.

.It is. to be 'understood thatthe Vform of the invention herewith shownand describeclris to be taken as` 2a :preferred example for fthe same,and that ivariouschanges .in itheisize', shape and arrangement of parts'may be :resorted to Ywithout departing .from `ithefspirit of my:invention or the scope .ofithefappendedeclaims. For example, .aplurality of furnaces inay 'be-aeiciently yoperated as a unit landiforlcertain .zpurposesdt may benacessary orfdesirable' .to falter :the size-or shape of the `respective parts.

:Havingthus :described my :inventiom I l claim:

f1. (A surface-:combustion:crackingfurnace iconiprisingfatlporouslrefractory tubeproviding :an interior surface for surfacecombustion deningr'a reactionfspece conduittor thesupplyofihydrocarbongas to be cracked opening into an end portion of said tube, an outletfrom the opposite end portion of said tube, a housing surrounding saidtube and spaced therefrom to provide a chamber therebetween, the wallsof said housing being otherwise sealed against passage of gas exceptthrough said porous refractory tube to the interior of the latter, agaseous mixture supply conduit opening into said chamber, two branched-conduits connected to said gaseous mixture supply conduit for thesupply under pressure of air and fuel gas respectively to said supplyconduit, means for proportioning the ratio of air to fuel gas passingfrom said branched conduits to said supply conduit to form a gaseouscombustible mixture in the latter in which the amount of oxygen is notin excess of that required for surface combustion of the fuel gas in thesaid combustible mixture, a pressure regulating valve for controllingthe pressure of the said gaseous combustible mixture, an additional flowcontrolling valve between said pressure regulating valve and saidchamber, and regulating means for said flow controlling valve eiectiveto control the flow of gaseous combustible mixture to said chamber inaccordance with the pressure of hydrocarbon gas in said firstmentionedconduit, whereby suiicient pressure difference is maintained betweensaid chamber and the interior of said tube to force the said gaseouscombustible mixture from said chamber inwardly through the pores of saidtube at a velocity greater than that of flame propagation outwardlythrough the pores of said tube, and the said gaseous combustible mixtureburns by surface combustion providing an incandescent lining at theinterior surface of said tube while the hydrocarbon gas passeslongitudinally through said tube within the incandescent lining and iscracked by the heat of said surface combustion.

2. A surface combustion cracking furnace according to claim 1, whereinthe said refractory tube has impervious end portions and a porouscentral portion, and sealing means between the impervious end portionsof said tube and said housing.

3. A surface combustion cracking furnace according to claim 1, whereinsaid tube is vertical, said inlet is at the lower end of said tube, saidAoutlet is at the upper end of said tube, and an expansion joint betweensaid housing and the lower end of said tube.

4. A surface combustion cracking furnace according to claim 1, includinga cooling jacket surrounding said outlet, and an inlet for directinjection of a quenching iiuid into said outlet.

5. A surface combustion cracking furnace according to claim l, whereinsaid tube is vertical, a supporting plate for the lower end of said tubereceiving said inlet, a sleeve slidably receiving the lower end of saidhousing, a retaining ring clamping said plate and sleeve together, anexpansion joint between said housing and said sleeve, said plate havingan opening therethrough communieating with the interior of said tube,and a removable closure for said opening.

EDWIN O. BENNETT.

REFERENCES CITED The following references are of record in the le ofthis patent:

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